Field device power supply failure detection

Abstract

To detect a power supply failure on an intrinsically safe field bus of a manufacturing process control system in an efficient manner there is provided a field device with a discharge protection unit which is connected to a control bus for supply of an operating current from the control bus to the field device. The discharge protection unit inhibits a discharge of energy stored in the field device to the control bus. The field device also comprises a controller unit adapted to control the operation of the field device and being powered with the operating current from the control bus. According to the present invention the discharge protection unit comprises at least two rectifying elements inserted into the current path of the operating current with identical conducting directions and an input signal or an output signal of a selected rectifying element is supplied as interrupt signal to the controller unit for power supply failure detection.

What is claimed is:  
     
       1. A field device for monitoring a manufacturing process and/or for actuating manufacturing process variables, the field device comprising: 
       a discharge protection unit connected to a control bus formed by a two-wire interface that provides an operating current supplying both a power signal for powering the field device and a communications signal for directing an operation of the field device, the discharge protection unit being adapted to supply the operating current from the control bus to the field device such that the discharge protection unit inhibits a discharge of energy stored in the field device to the control bus; and  
       a controller unit adapted to control the operation of the field device and being powered with the operating current from the control bus, the controller unit being operable to store control data related to an operation of the field device, using an internal memory of the controller unit;  
       wherein the discharge protection unit comprises at least two rectifying elements inserted into the current path of the operating current with identical conducting directions, and a signal associated with a selected rectifying element is supplied as an interrupt signal to the controller unit for power supply failure detection, such that the control data is stored within the internal memory in response to the power supply failure detection.  
     
     
       2. The field device of  claim 1  wherein the discharge protection unit is provided with an interrupt signal output terminal connected to the selected rectifying element. 
     
     
       3. The field device of  claim 1  further comprising an operating current modulating unit adapted to vary an effective resistance presented through the field device to the control bus and serially connected to the discharge protection unit for information exchange to/from the field device through operating current modulation under control of the controller unit. 
     
     
       4. The field device of  claim 2  further comprising an operating current modulating unit adapted to vary an effective resistance presented through the field device to the control bus and serially connected to the discharge protection unit for information exchange to/from the field device through operating current modulation under control of the controller unit. 
     
     
       5. The field device of  claim 3  further comprising a power conversion unit connected in series between the operating current modulating unit and the controller unit for supplying power to the field device. 
     
     
       6. The field device of  claim 1  wherein the discharge protection unit comprises three rectifying elements connected in series. 
     
     
       7. The field device of  claim 1  wherein the discharge protection unit comprises four rectifying elements connected in a full wave rectifier bridge network topology. 
     
     
       8. The field device of to  claim 7  wherein the discharge protection unit further comprises an additional rectifying element having an input connected to a bridge arm node of the full wave rectifier bridge and an output connected to the operating current modulation unit. 
     
     
       9. The field device of  claim 1  wherein: 
       the discharge protection unit comprises six rectifying elements connected in a full wave rectifier bridge network topology, wherein the full wave rectifier bridge has a first node and a second node connected to the control bus, a third node connected to a downstream circuit component of the field device, and a fourth node connected to ground;  
       a first rectifying element having a first conduction direction is inserted between the first node and the third node;  
       a second rectifying element having a second conduction direction is inserted between the fourth node and the second node;  
       a third and fourth rectifying element having the second conduction direction, respectively, are inserted between the first node and the third node; and  
       a fifth rectifying element and a sixth rectifying element having the first conduction direction are inserted between the third node and the second node.  
     
     
       10. The field device of  claim 9  further comprising a first resistor and a second resistor connected in series between a line connecting the third rectifying element and the fourth rectifying element and a line connecting the fifth rectifying element and the sixth rectifying element, wherein the signal at the network node between the first resistor and the second resistor is used as an interrupt signal at the interrupt signal output terminal. 
     
     
       11. The field device of  claim 1  further comprising a discharge protection element inserted in the line connecting the interrupt signal output terminal and the controller unit. 
     
     
       12. The field device of  claim 1  wherein each rectifying element and/or the discharge protection element is a diode. 
     
     
       13. A method of operating a field device for monitoring a manufacturing process and/or for actuating manufacturing process variables, the method comprising: 
       continuously monitoring a voltage on a control bus connecting the field device with a central controller or an operating current flowing from the control bus into the field device, where the control bus includes a two-wire interface that provides an operating current supplying both a power signal for powering the field device and a communications signal for directing an operation of the field device;  
       generating a power supply interrupt signal when the monitored voltage/operating current decreases beyond a predetermined first threshold (U B,min );  
       routing the power supply interrupt signal to a field device controller so as to circumvent an effective capacitance of the field device, such that a decrease in power being supplied by the control bus is detected at the field device controller without being substantially affected by a delay associated with the effective capacitance; and  
       saving internal states in an internal memory of a field device controller after supplying the power supply interrupt signal to the field device controller.  
     
     
       14. The method of  claim 13  wherein internal states of the field device controller are saved until the supply signal for the field device controller decreases beyond a predetermined second threshold (U o,min ) or data for all internal states are saved. 
     
     
       15. The method of  claim 13  wherein, upon receiving the power supply interrupt signal, the field device controller turns off power consumers in the field device to reduce power consumption. 
     
     
       16. The method of  claim 14  wherein, upon receiving the power supply interrupt signal, the field device controller turns off power consumers in the field device to reduce power consumption. 
     
     
       17. The method of  claim 13  wherein saving internal states is carried out according to a predetermined priority scheme. 
     
     
       18. The method of  claim 14  wherein saving internal states is carried out according to a predetermined priority scheme. 
     
     
       19. The method of  claim 15  wherein saving internal states is carried out according to a predetermined priority scheme. 
     
     
       20. A computer program product directly loadable into a memory of a field device controller, the product including software code for causing the field device to monitor a manufacturing process and/or to actuate manufacturing process variables, by causing the field device controller to: 
       continuously monitor a voltage on a control bus connecting the field device with a central controller or an operating current flowing from the control bus into the field device, where the control bus includes formed by a two-wire interface that provides an operating current supplying both a power signal for powering the field device and a communications signal for directing an operation of the field device;  
       generate a power supply interrupt signal when the monitored voltage/operating current decreases beyond a predetermined first threshold (U B,min );  
       route the power supply interrupt signal to a field device controller so as to circumvent an effective capacitance of the field device, such that a decrease in power being supplied by the control bus is detected at the field device controller without being substantially affected by a delay associated with the effective capacitance; and  
       save internal states in an internal memory of a field device controller after supplying the power supply interrupt signal to the field device controller.  
     
     
       21. The computer program product of  claim 20  wherein the software code causes internal states of the field device controller to be saved until the supply signal for the field device controller decreases beyond a predetermined second threshold (U o,min ) or data for all internal states are saved. 
     
     
       22. The computer program product of  claim 20  wherein, upon receiving the power supply interrupt signal, the software code causes the field device controller to turn off power consumers in the field device to reduce power consumption. 
     
     
       23. The computer program product of  claim 20  wherein the software code causes the saving of internal states to be carried out according to a predetermined priority scheme.